Understanding body language in reactive dogs

If you live with a reactive dog, you’ve probably been told to “watch the body language” — but that’s often easier said than done. Many behaviours commonly associated with aggression are actually signs of emotional overload, uncertainty or stress. When we understand this, we can respond more helpfully and reduce the pressure on both dog and human.  

Raised hackles (piloerection) 

In reactive dogs, raised hackles are frequently interpreted as a sign that a dog is about to “kick off”. In reality, piloerection simply tells us that the dog’s emotional arousal is high. This might be due to excitement, anxiety, frustration, or a combination of all three. Real life example: A reactive dog spots another dog at a distance. Their hackles rise, but they are still able to eat treats, respond to their handler, and move away. This tells us the dog is coping, even if they’re highly stimulated. Hackles alone don’t predict what will happen next — behaviour does.  

Tail wagging 

Many reactive dogs wag their tails during reactions, which can be confusing or even alarming to owners. A wagging tail in this context does not mean the dog is happy about the situation. Real life example: A dog lunges and barks at another dog while their tail is high, stiff and wagging rapidly. This wag reflects tension and arousal, not friendliness. Understanding this helps owners recognise early signs of escalation rather than assuming their dog is “fine”. 

Showing teeth 

Reactive dogs may show teeth in a range of ways, and not all of them are threats — but context is crucial. Real life example: A dog that curls their lip while freezing and staring is offering a clear warning signal and needs space. In contrast, a dog who flashes teeth briefly while remaining loose and wiggly during a gree ng may be showing appeasement rather than intent to bite. Misreading these signals can lead to dogs being pushed past their comfort zone.  

Why this matters for reactive dogs  

Reactive behaviour is often the result of a dog being over threshold — emotionally overwhelmed and struggling to cope. When we focus on single signals, we miss the opportunity to intervene early. By observing the whole dog — their ability to disengage, take food, move freely, and recover — we can make be er decisions about distance, management and training. This not only improves safety, but helps reactive dogs feel more understood and supported. Reactivity isn’t about “bad behaviour”. It’s communication — and learning to listen is one of the most powerful tools we have.